Regioregular dithienosilole- and dithienogermole-based small molecules with symmetric distal/distal orientation of F atoms

摘要

This study describes the synthesis and characterization of a series of regioregular dithieno(3,2-b;2',3'-d)-silole (DTSi)and dithieno(3,2-b;2',3'-d)-germole (DTGe)-based small molecules-7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-b:4,5-b']dithiophene-2,6-diy1)bis(5-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-Abenzo[c][1,2,5] thiadiazole) (DTSi(B 1112)0, 7,7'-(4,4-bis(2-ethylhexyl)-4H-germolo dithiophene-2,6-diAbis(5-fluoro-4-(5'-hexyl-[2,2'-bithiophen]-5-y1) benzo[c] [1,2,5]thiadiazole) (DTGe(BTFTh2)(2)), 7,7'-(4,4-bis(2-ethylhexyl)-4H-silolo[3,2-6:4,5-bldithiophene-2,6-diy1) bi-s(4-(benzofuran-2-yl)-5-fluorobenzo[c] [1,2,5]thiadiazole)(DTSi(BTFBF2)(2)), and 7,7'-(4,4-bis(2-ethylhexyl)-4H-germolo[3,2-6:4,5-bldithiophene-2,6-diy1)bis(4-(benzofuran-2-yl)-5-fluorobenzo[c] [1,2,5]thiadiazole) (DTGe(BTFBFu)2) (D'I'Si(BFTTh2)(2), DTGe(BFTTh2)(2), DTSi(BFTTu(2))(2), and DTGe(BFTTu(2))(2) in which two F atoms are in a symmetric distal/distal configuration relative to the central core units. The optical and electrochemical properties are strongly influenced owing to changes of the terminal units (BFu and Th-2) rather than by the tuning of the core units (DTSi and DTGe). In addition to a high fraction of the edge-on orientation in the neat films of all of the molecules, the presence of hexyl side chains in the Th-2 terminal units are found to play a critical role in forming high-quality films, leading to homogeneous and smooth surfaces in the films of Th-2-containing molecules. When used as donor materials in small-molecule:fullerene solar cells, the best power-conversion efficiency of 3.26% was achieved with the DTSi(BTFTh2)(2)based system. Our study herein provides a relevant step toward understanding such isomorphic small molecules.